1. Field of the Invention
The present invention relates to collet chucks for holding a tool or workpiece on a spindle of a turning machine.
2. Description of Related Art
Collet chucks are used to clamp or grip workpieces or tools in turning machines, such as lathes. The collet head inside the chuck includes a number of circumferentially-spaced gripping segments and a number of cam surfaces. When the collet head is moved axially, its cam surfaces interact with corresponding opposing surfaces or cams on the mounting fixture. The interaction of the opposing cam surfaces causes the gripping segments of the collet head to expand or contract, thus causing it to grip or release a workpiece or tool, depending on the direction of axial movement.
Collet chucks are commonly used in place of other types of chucks, especially for smaller workpieces, because they are typically more accurate and can transmit more torque than a conventional chuck, such as a jaw chuck. Another advantage of collet chucks is that they maintain their grip at high rotational speeds, whereas the centrifugal forces present at high rotational speeds may cause a conventional jaw chuck to loosen its grip on the workpiece.
In conventional collet chucks, the axial movement required to grip the workpiece also moves the workpiece. This can be undesirable, because variations in diameter from workpiece to workpiece may result in variations in workpiece position, since the position at which the workpiece is grasped depends on the difference in diameter between the open collet head and the workpiece.
DEAD-LENGTH(trademark) collet chucks are often used to eliminate the inconvenience associated with collet head axial movement. In such chucks, the collet head is held in an axially fixed position while a selectively axially moveable collet closing sleeve is moved. The collet closing sleeve has cam surfaces which engage those of the collet head, forcing the collet head to open or close, depending on the collet closing sleeve""s direction of movement. Typically, collet closing sleeves are moved forward to close the collet head and rearward to open it.
In most DEAD-LENGTH(trademark) collet chucks, the collet head gripping segments are held in an axially fixed position by a cap which is bolted or otherwise secured to the forward end of the collet closing sleeve. The collet head segments bear against the cap, and since they cannot move forward because of the cap, they are forced to either open or close in response to movement of the collet closing sleeve. When the collet head needs to be changed, for example, to replace the seals between segments, the cap must be removed. Although some caps are designed for quick removal and replacement, the cap is an intricate part and its removal may be an inconvenience to the user.
DEAD-LENGTH(trademark) collet head is typically mounted on the spindle of a user""s turning machine and is connected to the draw bar of the machine. The link-up components that connect the collet closing sleeve to the user""s spindle and draw bar may need to be specially fabricated for each user""s machine.
One aspect of the invention relates to a collet chuck assembly with an axially fixed collet head. The collet chuck assembly comprises a spindle adapter body, a sleeve assembly, one or more resilient elastic members and a bushing member.
The sleeve assembly of the collet chuck assembly has outer surfaces constructed and adapted to slidingly engage corresponding inner surfaces of the spindle adapter body. This sliding engagement facilitates axial movement along a collet assembly movement axis. The sleeve assembly defines an interior collet head receiving passage which has engaging, motion-translating surfaces on at least a portion. The sleeve assembly also comprises a rear portion having one or more bearing surfaces extending perpendicularly with respect to the collet assembly movement axis. A set of projections extend from the rear portion substantially parallel to the collet assembly movement axis. Resilient elastic members are installed between the bearing surfaces of the sleeve assembly and corresponding bearing surfaces of the spindle adapter body. A bushing member is constructed and arranged to be removably and fixedly mounted within the interior cavity of the spindle adapter body proximate to the sleeve assembly. The bushing member has a central passage positioned and adapted to be operationally contiguous with the collet head receiving passage of the sleeve assembly. The central passage has structure constructed and arranged to secure a collet head against movement along the collet assembly movement axis. The bushing member also defines one or more passages arranged to receive the projections of the sleeve assembly so as to place the sleeve assembly in motion-transmitting relation with motion-generating or transmitting structures connected to the turning machine.
Another aspect of the invention relates to a turning machine. The turning machine comprises a spindle, a drawbar, and the collet chuck assembly described above.
A further aspect of the invention relates to an actuation mechanism for a collet head. The actuation mechanism comprises a sleeve assembly adapted to move between first and second positions along a first movement axis, the first position establishing an open position of the collet head and the second position establishing a closed position of the collet head. The sleeve assembly has engaging, motion-translating surfaces constructed and arranged to engage corresponding surfaces of the collet head. The sleeve assembly also has projections constructed and arranged to be inserted through a fixed member so as to transmit motion to the sleeve assembly. Additionally, the actuation mechanism comprises one or more resilient elastic members that are adapted to bear against an outer surface of the sleeve assembly and a bearing surface of another structure while resiliently resisting movements of the sleeve assembly between the first and second positions.
These and other aspects of the invention will be described below in greater detail.